1. Field of the Invention
This invention relates to a brushless motor using permanent magnets and electromagnetic coils.
2. Description of the Related Art
In the motor industry, both one-phase motors and two-phase motors are collectively called “single phase motors.” However, with the description below, “single phase motor” means only one-phase motors, and excludes two-phase motors.
A brushless motor using permanent magnets and electromagnetic coils is disclosed, for example, in JP2001-298982A.
With this prior art brushless motor, control is performed using on/off signals from digital magnetic sensors. In specific terms, the timing of the polarity inversion of the applied voltage to the electromagnetic coils is determined using the on/off signals of the digital magnetic sensors. Also, three-phase drive signals are used as the drive signals.
From the past, there has been a desire for improved efficiency of various types of motors including brushless motors. However, as a result of improvements in motors over many years, in recent years, it has become difficult to find new mechanisms for improving motor efficiency.
Regarding brushless motors, there have further been the following kinds of problems. Specifically, with conventional brushless motors, drive signals of two or more phases are used, and there are no motors using single-phase drive signals. The reason for this is related to the startup characteristics of the single-phase motor described hereafter.
The single-phase motor has the characteristic of not being able to start up when the permanent magnets and coils stop at directly facing positions. This position is called the “deadlock point” or the “dead point.” Because of this, with the normal single-phase motor, an auxiliary coil is provided for reliably performing startup, and a startup method is used whereby current is flowed to the auxiliary coil only during startup. Also, with certain types of single-phase motors, a capacitor is used to displace the phase of the main coil and the auxiliary coil.
Meanwhile, with a normal brushless motor, a so-called inverter drive is used. However, when the single-phase motor is started up using inverter drive, a large current is flowed to the auxiliary coil or capacitor during startup, so the problem arises of damage to the switching component and capacitor occurring easily. In this way, there has been the problem that constituting the single-phase motor as a brushless motor is difficult.